1. Field of the Invention
The present invention relates to an optical semiconductor module comprising an optical element composed of a light emitting element (a laser diode: LD) or a light receiving element (a photodiode: PD), and an optical fiber optically connected to the optical element; and a process for producing the same. The present invention relates specifically to an optical semiconductor module making it possible to attain airtight sealing easily and surely, and a process for producing the same.
2. Description of the Related Art
As optical fiber communication has been spreading recently, for an optical semiconductor module used in the optical fiber communication, a low-priced module whose assembly process is made simple has been demanded. For this purpose, there is generally used a module wherein a semiconductor laser element as a light emitting element and an optical fiber are mounted on a single Si substrate. In this case, the strand of the optical fiber is bonded to a xe2x80x9cVxe2x80x9d-shaped groove made in the Si substrate at a given position with a resin or a solder material (such as AuSn) as an adhesive agent, and is fixed with an optical fiber-pressing plate. The optical fiber is drawn out from an optical fiber drawing-out mouth made in a housing to the outside of the housing. As a sealing material for the optical fiber drawing-out mouth, there is used a solder paste comprising AuSn, PbSn or the like, a low melting-point glass or a resin.
However, in the case that the solder paste is used, in order to enhance close adhesion between the optical fiber and the solder paste, it is necessary that a surface of the optical fiber is subjected to metal processing such as Au plating. Thus, the number of processing steps increase. For this reason, the optical semiconductor module becomes high-priced. In the case that the low melting-point glass is used, it is necessary to heat the optical fiber drawing-out mouth up to 430-470xc2x0 C., at which the low melting-point glass is melted. Therefore, the solder paste with which the optical fiber is fixed to the substrate in the housing is melted so that the positional relationship between the semiconductor laser and the optical fiber gets off. As a result, there arises a problem that a desired optical fiber output cannot be obtained.
Thus, Japanese Patent Application Laid-Open No. 9-69585 discloses a process using resin as a process for sealing an optical fiber drawing-out mouth. FIG. 6 is a sectional view showing a conventional optical semiconductor module in the Japanese Patent Application Laid-Open No. 9-69585. In this conventional optical semiconductor module, a part of a semiconductor laser array 301 is fixed to a xe2x80x9cVxe2x80x9d-shaped groove formed in a Si substrate 303. An optical fiber array 343 is fixed to the Si substrate 303 with a fiber array-pressing plate 306 on the array 343. The Si substrate 303 is fixed to a bottom of a case 308 with AuSn solder paste. A cap 309 is located on the case 308. A fiber drawing-out mouth 310 is made in a housing composed of the case 308 and the cap 309. One end of the optical fiber array 343 is drawn out from the fiber drawing-out mouth 310 to the outside of the housing.
Thermosetting resin 312 is beforehand applied to the fiber drawing-out mouth 310. By heating the case 308 and the cap 309, the thermosetting resin 312 is cured to seal the fiber drawing-out mouth 310. Grooves 311 for storing liquid resin are made in the fiber drawing-out mouth 310 in such a manner that the thermosetting resin 312 does not leak out by the thermal expansion of the inside of the housing.
Japanese Patent Application Laid-Open No. 9-148592 discloses a process for sealing such a fiber drawing-out mouth as above, using resin having both photo-curing and thermosetting properties.
However, in the conventional optical semiconductor module disclosed in the Japanese Patent Application Laid-Open No. 9-69585, the structure of the optical fiber drawing-out mouth 310 formed in the case 308 and the cap 309 is complicated. Therefore, the number of steps for producing the case 308 and the cap 309 is increased. Thus, there arises a problem that the optical semiconductor module becomes high-priced. Since the thermosetting resin 312 does not flow uniformly into the grooves 311 for storing liquid resin, air bubbles are incorporated into the thermosetting resin 312. Thus, when the resin 312 is cured, air-releasing paths are formed inside the resin 312. Therefore, moisture enters easily from the outside to the inside of the optical semiconductor module via these air-releasing paths. Thus, there also arises a problem that the optical semiconductor element (the laser array 301) inside the optical semiconductor module 300 is broken and the reliability thereof drops.
The process disclosed in the Japanese Patent Application Laid-Open No. 9-148592 has a problem that the number of assembly steps increases by the double process composed of an photo-curing process based on irradiation with ultraviolet rays and a thermosetting process so that the optical semiconductor module becomes high-priced.
An object of the present invention is to provide an optical semiconductor module making it possible to attain airtight sealing easily and surely and improve reliability at a low price; and a process for producing the same.
According to one aspect of the present invention, an optical semiconductor module comprises: a housing having an opening; an optical semiconductor element provided in the housing; an optical fiber that penetrates the opening, the optical fiber performing optical transmission between the optical semiconductor element and an element arranged outside the housing; photo-curing resin sealing the opening; and a transparent plate arranged between the photo-curing resin and the outside of the housing.
Since the opening that the optical fiber penetrates is sealed with the photo-curing resin in the present invention, air bubbles and the like are not produced and airtight sealing is certainly ensured. Thus, the reliability of the module is high. Since ultraviolet rays are radiated to the photo-curing resin through the transparent plate so that the photo-curing resin is cured, the number of producing steps can be decreased and costs can be reduced.
In the present invention, the housing may comprise a case on which the optical semiconductor element is put, and a cap fitted onto this case, and the difference between the linear expansion coefficient of the photo-curing resin and that of the case may be less than 1xc3x9710xe2x88x925/xc2x0C. By setting the difference between the linear expansion coefficients to less than 1xc3x9710xe2x88x925/xc2x0C., it is possible to prevent generation of cracks based on a change in external temperature or the like, and improve certainty of airtight sealing.
The light transmission ratio of the transparent plate may be equal to or more than 98%. By setting the light transmission ratio of the transparent plate to 98% or more, it is possible to cure the photo-curing resin for fixing the optical fiber core line still more easily.
The opening may comprise a concave opening portion having at least two stages, and the optical fiber and the transparent plate may be arranged on different stages from each other.
According to another aspect of the present invention, the process for producing an optical semiconductor module comprises the steps of: putting an optical semiconductor element inside a case; and arranging an optical fiber in the case. The optical fiber performs optical transmission between the optical semiconductor element and an element arranged outside the case. The process further comprises the steps of: providing photo-curing resin to areas where side walls of the case and the optical fiber cross each other; putting a transparent plate on the photo-curing resin; and radiating light onto the photo-curing resin through the transparent plate to cure the photo-curing resin.
In the process according to the present invention, the optical fiber is fixed to the case by curing the photo-curing resin. Thus, the number of producing steps is reduced, and air bubbles are not incorporated so that the reliability of the module is high.
In the process, the difference between the linear expansion coefficient of the photo-curing resin and that of the case may be less than 1xc3x9710xe2x88x925/xc2x0C., and the light transmission ratio of the transparent plate may be equal to or more than 98%.